Extrusion apparatus with removable die insert



June 29, 1965 w. H. STULEN 3,

EXTRUSION APPARATUS WITH REMOVABLE DIE INSERT Filed Aug. 28. 1962 3Sheets-Sheet l INVENTOR. WALTER H. STULE/V ATTORNEY EXTRUSION APPARATUSWITH REMOVABLE DIE INSERT Filed Aug. 28, 1962 June 29, 1965 w. H. STULEN3 Sheets-Sheet 2 United States Patent 3,191,413 EXTRUSION APPARATUS WITHREMOVABLE DIE INSERT Waiter H. Stulen, North Caldwell, NJ., assignor toBaldwin-Lima-Hamilton Corporation, Philadelphia, 2a.,

a corporation of Pennsylvania Filed Aug. 28, 1962, Ser. No. 219,917

23 Claims. (CI. 7241) This invention relates to an extrusion apparatus,and more particularly to an extrusion apparatuswherein the extrusion dieis provided with a removable insert.

A-substantial amount of time, effort and money has been expended withinrecent years in order to explore the concept of using a ceramic orcermet insert in an extrusion die. As a result of all of this researchwhich has been conducted heretofore, the conclusion of all partiesassociated with the project was to the effect that ceran'iic or cermetinserts at the throat of an extrusion die orifice is not practical dueto the low tensile strength of the insert.

It has been recognized heretofore that an extrusion die having a ceramicinsert at the throat of the orifice is desirable. A die having such aninsert would enable extrusions to have a smoother finish, extrusions maybe accomplished-at higher temperatures, and the life span of the diewould be substantially increased. While all of the evidence heretoforeindicates that ceramic inserts in an extrusion die are impractical, Ihave found that the main stumbling block, namely the low tensile andimpact strength of the ceramic, can be avoided in a manner which issimple, inexpensive and reliable.

In the extrusion apparatus of the present invention, the extrusionorifice ofthe die is the inner diameter of an annular ceramic or cermetinsert. The insert is mounted in a well in the die. The diameter of thewell is slightly greater than the diameter of the insert so that anannular chamber having a width of between about .003 inch to .007 inchis provided between the walls defining the well and the outer diameterof the insert. Means are provided to facilitate the introduction of amovable medium such as a lubricant, insulating fluid, etc., into a lowpressure zone on the land of the die adjacent the well. At the end ofthe stroke where the flowing metal approaches zero velocity, suchflowing metal applies a pressure to the medium so that the forcesexerted in a radial direction on the insert during the instantaneousapproach to zero velocity of the flowing metal are balanced. U r

The introduced medium into the low pressure zone on the land of the dieor in the container assembly liner ad: jacent the die facilitates theintroduction of a lubricant during the extrusion process notwithstandingthe fact that pressures with-in the container assembly may approach150,000 pounds per square inch when extruding steels. Since thelubricant medium is introduced into a low pressure zone, it maygenerally be pumped thereint-o at a pressure below 400 pounds per squareinch. In order to preventthe flowing metal from bypassing the dieorifice as the flowing metal approaches zero velocity at the end of theextrusion stroke, the conduit system for conveying the lubricant mediumto the die is provided with a line condition responsive valve whichautomatically closes. Since the lubricant medium is incompressible, orsubstantially so, the flowing metal will not enter the low pressure3,191 ,413 Patented June 29, 1965 zone notwithstanding the fact that theflowing metal is free from laterally restrictive forces in the lowpressure zone.

It is an object of the present invention to provide a novel apparatusand method for extruding materials.

It is another object of the present invention to provide a novelapparatus and method for extrusion of hard materials such as steel,stainless steel, titanium, etc.

It is another object of the present invention to provide an extrusionapparatus wherein the die is provided with a ceramic or cermet insert atthe orifice.

It is still another object of the present invention to provide a novelextrusion die wherein the orifice thereof is formed by a ceramic orcermet insert.

It is a still further object of the present invention to provide a novelextrusion apparatus or method wherein the radial compressive forces on adie insert are substantially balanced.

It is still another object of the present invention to provide a novelextrusion apparatus or method wherein an extrusion die is provided witha low pressure zone adjacent the outer periphery of a die insert tofacilitate the ease with which an extrusion process may be accomplishedand to facilitate the flow of a medium between the die and the insert toequalize radial pressures on the insert as flowing metal approaches zerovelocity.

It is yet another object of the present invention to provide a novel diefor use in an extrusion apparatus or method.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in thedrawings forms which are presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIGURE 1 is a top plan view of an extrusion apparatus in accordance withthe present invention.

FIGURE 2 is a longitudinal sectional view of the container assemblyillustrated in FIGURE 1.

FIGURE 3 is a partial sectional view similar to FIG- URE 2, butillustrating another embodiment of the present invention.

FIGURE 4 is a sectional view of a die in accordance with anotherembodiment of the present invention.

FIGURE 5 is .a partial sectional view of the die in FIG- URE 4 as theflow metal reaches 'zero velocity.

Referring to the drawing in detail, wherein like numerals indicate likeelements, there is shown in FIGURE 1 an extrusion apparatus designatedgenerally as 10.

The extrusion apparatus 10 includes a container assembly 12 having abore therein which is adapted to receive a reciprocably mounted stem 14.Stem 14 is provided with a dummy block 16 and a removable mandrel 18.The stem 14 is supported by a crosshead 20 and is connected to .a pistonor ram disposed within the main cylinder 22. Whenthe stem 14 is' causedto reciprocate to the left in FIGURE 1 under the pressure in thecylinder 22, the crosshead 20 is guided and supported by guide members24 and 26.

The container assembly 12 includes a cylindrical liner 28 having a mainbore 30. As shown more clearly in FIGURE 2, the main bore 30 is providedwith an enlarged diameter portion 32 at the lefthand end thereof. Areduced diameter portion of a die 34 is received within the portion 32of the liner 28. Means, not shown, will be provided to maintain therelationship between the die 34 and liner 28.

. The inlet side of the die 34 is provided with a converging land 35which applies a radially constrictive force on the material to beextruded thereby directing the same toward the extrusion orifice 37. Theextrusion orifice 37 is backed up by relief bores 38 and 40.

The die 34 is provided with a well 42 concentric with the bores 38 and40. The diameter of well 42 is greater than the diameter of bore 38thereby providing a radially outwardly directed shoulder 44. A dieinsert 46 is disposed within the well 42 and is in abutting contact withthe shoulder 44. The extrusion orifice 37 is the inner diameter of theinsert 46.

The insert 46 is provided with a converging land 48.

The difference in the angle of convergence of lands 36 and.

48 results in a rapidly changing contour of the surface exposed to theflowing metal thereby providing an annular low pressure zone 50. Theouter diameter of the insert 46 is smaller than theinner diameter of thewell 42 thereby resulting in an annular zone having a width of between.003 inch and .007 inch. .This annular zone is in communication with thelow pressure zone 50.

A means is provided to facilitate the introduction of a medium such as alubricant, a separator material, etc. into the low pressure zone 50.Such means includes flow passages 52 and 54 which extend through the die34. Conduit 56 is in communication with passage 52 to facilitate theintroduction of a medium thereinto. Conduit 56 is preferably providedwith a one-way line condition responsive valve such as check. valve 55.Conduit 58 is in communication with passage 54 to facilitate theintroduction of a medium thereinto. Conduit 58 is provided with aone-way line condition responsive valve such as check valve 57. Thepurpose of valves 55 and 57 will be made clear hereinafter.

When making a solid extrusion, the mandrel 18 will be removed so thatthe stem 14 terminates in a dummy block 16 having an imperforate metalengaging face. When it is desired to produce a hollow extrusion, amandrel 18 will be provided. Mandrel 18 may have an enlarged diameterportion 62 at the end thereof adjacent the dummy block 16. The rapidchange in the diameter between portion 62 and the remainder of themandrel 18 results in the provision of a low pressure zone 64. P35?sages 66 and 68 may be provided through thestem 14, dummy block 16, andportion 62 so that a medium may be introduced into zone 64. The lowpressure zone 64 is an area at which the flowing metal laterallyrestrictive forces.

The operation of apparatus is as follows:

A billet or the like will be disposed within the liner 28. When thebillet is a hard metal such as steel, the billet will be at atemperature approximating 2200 F. Pressure on the piston in cylinder 22will cause the stem 14 and dummy block 16 to reciprocate to the left inFIG- URES 1 and 2 thereby exerting a substantial amount of pressure onthe billet to cause the same to flow toward the die orifice. The flowingmetal is designated as 60 in FIGURE 2. As the flowing metal 60 contactsthe land 36, it is subjected to radially constrictive forces and itsvelocity is increased rapidly. Due to the velocity of the flowing metal60, it does not enter the low pressure zone 50 but merely continues onto the throat of the orifice 37.

Since the flowing metal 60 is free of radially constrictive forces as itpasses the low pressure zone 56 a lubricant or other medium may beintroduced through the passages 52 and 54 to ease the extrusion of themetal 60 and/or protect the die. The medium introduced into zone 50 maybe pressurized to a pressure as low as 400. pounds per square inch. Suchmedium flows into the space between the insert 56 and the axiallyextending wall of well 42. As the flowing metal 6i} approaches zerovelocity at the end of the stroke, the flowing metal exerts will be freeof a substantial amount of pressure on the medium in zone 50 andpassages 52 and 54. The back pressure on the lubricant medium will closethe valves 55 and 57 thereby preventing loss of the flowing metaL' Whenthe hot extrusion metal contacts the lubricating medium such as grease,instant flashing and vaporization of the medium occurs since the flashpoint is well below the temperature of the metal and the resultantpressure of the medium exerts a radially inwardly directed pressure onthe insert 46 which substantially equalizes with the pressure exertedradially outwardly on the insert 46 by the flowing metal 60 as it isbeing extruded. These actions are accomplished almost instantaneouslyas-the flowing metal approaches zero velocity.

Test run with ceramic die inserts have'indicated that the failure of theceramic inserts took place at the end of the stroke. The provision of ameans for equalizing the radial pressures on the insert 46 preventsfailure of the insert in compression. The insert 46 may be f a materialcommonly referred to as a ceramic or a cermet. A ceramic is a claybearing material capable of being fired. A cermet is a ceramic havingmetallic particles therein. I have obtained excellent results with aninsert 46 made from aluminum oxide fired to 2750 F.

It will be appreciated by those skilled in the art that a wide varietyof ceramic materials may be utilized for the die insert an. The body ofthe die'34 may be a metal, a ceramic, or a cermet. The medium introducedthrough the passages 52 and 54 to tr e low pressure zone 54 may includegrease, flaked graphite, soapstone, mica, any one of a Wide variety ofinsulating materials, etc. At the end of the extrusion cycle, I havefound it advisable to flow pressurized air through-conduits 5d and 58,passages 52 and 54 respectively, to the lowpressure zone 50 to clear thesame prior to the next extrusion cycle.

The insert 46 will maintain the tolerances of the orifice 37substantially longer than a conventional die. When the insert 46 showsindications of wear, it is capable of being readily replaced withanother insert. The ability to substitute an inexpensive insert greatlyreduces the cost incident to replacement parts subject to wear in anextrusion apparatus.

When it is desired to extrude a hollow extrusion 61, a mandrel 18 willbe provided which may have a separate actuator in addition to beingresponsive to movement of stem 14. The manner in which the mandrel 18pierces the billet thereby initiating the inner diameter of theextrusion 61 is conventional and need not be described in detail. Whenextruding a hollow member such as extrusion 61, the above description asto the operation in relation to the outer diameter of extrusion 61occurs. Further, the flowing metal 60 as it passes the low pressure zone64 is free of radially constructive forces on the inner diameter of theflowing metal. A lubricant or other medium may be introduced throughpassages 66 and 68 to the low pressure zone 64 thereby facilitating theease with which the extrusion 61 may be produced and increasing'the lifespan of the surfaces of the tools which contact the flowing metal 60during the extrusion process.

In FIGURE 3, there is disclosed another embodiment of the presentinvention wherein a die 34' may be substituted for the die 34. The die34' is provided with a well 42'- concentric with bore 38'. An insert 46made from a clay bearing material capable of being fired is disposedwithin the well 42' in the same manner as described above. The land 36is provided with a low pressure zone '70 having a passage 54' incommunication therewith as .described above.

The insert 46 is provided with a groove 72 on its outer peripheralsurface to increase the width of the annular space between the peripheryof the insert 46' and the axially extending surface of the well 42. Thisincrease is necessitated by the high viscosity of certain lubricants orinsulating mediums which are to be introduced into the low pressure zone70. The high viscosity of these mediums requires the space into whichthey areto flow to be substantially greater than the figures mentionedabove. When the space is increased so as to facilitate the introductionand flow of high viscosity mediums into the space between the insert 46'and the axially extending surface of the well 42', the insert 46'becomes too loose. The desired tightness of the insert within the well42' is accomplished by the provision of the groove 72. The fact that theinsert 46 or 46' may not be exactly concentric with the bore 38 prior tothe commencement of the extrusion process is of no moment since the flowof the metal through the orifice in the insert 46 will automaticallycentralize the insert 46 or 46.

As illustrated more clearly in FIGURE 3, the die orifice nee-d not beonly the inner diameter of the insert 46 or a portion thereof, but mayincude the bore 38'. In this case, bore 40' will be the only reliefbore.

The liner 28 and the container there'around may be provided with apassage 74 which is in communication with a low pressure zone 76 formedat the intersection of surfaces defining land 36 and portion 32 of thebore 30. The introduction of a lubricating o1- insulating medium intozone '76 facilitates the ease with which the flowing metal 60 will flowacross surface 36' thereby increasing the useful life of die 34. Allother features, characteristics or operation of the embodimentillustrated in FIGURE 3 may be identical as that described above andtherefore need not be described in detail.

In FIGURES 4 and 5, there is disclosed another embodiment of a diehaving a ceramiciinsert which may be substituted for the die and insertillustrated in FIG- URES 13. The die in FIGURES 4 and 5 is designatedgenerally as 34" and is identical with die 34 except as will be madeclear hereinafter.

The die 34" is adapted to be utilized in conjunction with a containerassembly such as assembly 12, and a reciprocally mounted stem such asstem 14. The die 34" is provided with a converging land 36 which appliesa radially constrictive force on the material to be extruded therebydirecting the material toward the extrusion orifice. r r

The land 36 terminates at its most radially inwardly point in an axiallyextending bore 80. Die 34" is provided with a second axially extendingbore 8 8 having a larger diameter than bore '80 and separated therefromby a shoulder 82. A'die insert designated generally as 83 isreciprocally supported within the bore 88. Insert 83 is provided with anannular end face '84 juxtaposed to the shoulder 82. The outer peripheralsurface of the insert '83 is spaced from the bore 88 thereby defining anannular channel 89 therebetween.

The corner of the die insert 83 adjacent endface 84 is provided with aplurality of serrations 90 which provide communication between thechannel 89 and a low pressure zone resulting from the angulardisposition of bore 80 and the converging land 92 on the insert 83.Insert '83 may be made of the same material as inserts 46 and 46. Insert83 is provided with a bore 94 constituting the orifice or throat of thedie 34".

The insert 83 is provided with an end face 96 at the end thereofopposite from end face 84. A first backup ring 98 is provided within athird bore of the die 34". Backup ring 98 is recessed to receive aportion of the insert 83 and has a bore therethrough which functions asa relief for the orifice in insert 83.

Backup ring 98 is provided with an annular groove 100 on one facethereof and juxtaposed to the end face 96 on insert 83. The backup ring98 is provided with a large annular groove 100 on the opposite face fromthat containing the groove 100. A plurality of passages 104 extendthrough the ring 98 providing communication between the grooves 102 and100. A conduit 106 extends through a portion of die 34" and is incommunication with groove 102. A backup ring 108 maintains thebackupjring 9 8 in the illustrated position.

The embodiment illustrated in FIGURES 4 and 5 functions in the samemanner as the embodiments illustrated above except as will be made clearhereinafter. Immediately before initiating the extrusion of thematerials, lubricant, coolant, or other flowable medium may beintroduced through conduit 106, groove 102, passages 104, groove 100,channel 89, and serrations into the low pressure zone. a

The end face of the insert 83 will be juxtaposed to and abutting theshoulder 82 as a result of the pressure of the lubricant acting againstthe end face 96. The surface area on end face 96 which is subjected tothe pressure of thelubricant is substantially greater than the surfacearea at the orifice subjected to the pressure of the flowing materialwhich is being extruded. Any gases generated by contact between alubricant and the flowing material may build up pressure. Such pressurewill reciprocate the die insert 83 to the left in FIGURE 4 so that theelements assume the position illustrated in FIGURE 5. Such movementofthe insert'83 interrupts the introduction of lubricant'or other mediuminto the low pressure zone. Hence, the insert 83 acts as a valve member.After the gases dissipate themselves, the com ponents will resume theposition illustrated in FIGURE 4.

As the flowing metal reaches zero velocity, the pressure of the flowingmetal on the insert 83 is greater than the pressure of the lubricant orflowable medium acting against end face 96. Hence, the insert 83 willreciprocate to the left thereby assuming the position illustrated inFIGURE 5. Also, the lubricant trapped in channel 89 will bepressurizedby the flowing material so that the insert '83 will besubjected to equalized or balanced radial forces. 1

The reciprocatory movement of the die insert 83 may be obtained byeliminating the shoulder 82, if desired. The flowing material willperform the function of shoulder 82 if the initial introduction oflubricant or other flowable medium is timed so as to occur atsubstantially the same time as the flowing metal contacts the land 36".Q Any one of the embodiments of the die and removable insert-of thepresent invention may be utilized on an inverse'extrusion press. Hence,the dies with their inserts will be supported by the moving ram insteadof being stationary as illustrated. Either arrangement is considered tobe within the scope of the claims set forth hereinafter. Hence, it willbe seen that I have invented an apparatus and method wherein extrusionof hard metal such as steel as well as easy to extrude materials may bemore easily accomplished as a result of the creation of low pressure,zones into which a lubricant 0r insulating medium may be introduced tocoat the outer and/or inner surface of the flowing metal prior to andduring the passage of the flowing metal through the die ori fice. Thedie orifice may be the inner diameter of an annular die insert made froma clay bearing material capable of being fired, and commonlyreferred toas a ceramic or cermet.

The die insert is structurally interrelated with the die so thatcompressive forces in a radial direction are substantially balanced atthe end of the stroke when the flowing metal approaches zero velocitythereby preventing failure of the insert. A valve means is provided inthe flow line for the lubricating or insulating medium to prevent theflowing metal from bypassing the die orifice. The die insert is capableof being readily removed and a new die insert may be substitutedtherefor. The simplicity and low cost of the apparatus and method of thepresent invention overcomes many disadvantages of the prior art whileincreasing the quality of the surface finish on the extruded parts,decreases the amount of ram pressure in the main cylinder, facilitatesthe extrusion of hard metals, increases the useful life of the die,facilitates the replacement of only the orifice hearing portion of thedie thereby decreasing the cost of replacement parts, eliminates excesshandling of ingots and extruded parts associated with the prior art, andfacilitates the extrusion of metals at higher temperatures than thosecontemplated or practical with the devices proposed heretofore.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of the invention. 7

I claim: '1. In an extrusion apparatus comprising a container assemblyadapted to support a billet therewithin, a die means having an orifice,ram means associated with said assembly for applying pressure on abillet in the container assembly to force the billet to flow throughsaid orifice, means for providing a low pressure zone wherein theflowing material of the billet is free of laterally restrictive forces,said die means having an annular die insert made from a clay bearingmaterial capable of being fired, and means for introducing a flowablemedium into said low pressure zone and around said die insert so thatthe flowable medium is between the periphery of said insert and thejuxtaposed portion of said die means.

2. In an apparatus in accordance with claim 1 wherein the orifice of thedie means is the inner diameter of the insert.

3. In anapparatus in accordance with claim 1 wherein said insert is aceramic.

4. In an apparatus in accordance with claim 1 wherein said insert is acermet.

5. In an apparatus in accordance with claim 1 wherein the outerperiphery of said insert is provided with a radial: 1y inwardly directedgroove adapted to be in contact with the flowable medium.

6. In an apparatus in accordance. with claim 1 wherein said die meanshas a radially inwardly converging land which causes the velocity offlowing metal to increase rapidly, and means providing a low pressurezone upstream of said land, and passage means extending through saidcontainer assembly into communication with said last mentioned zone tofacilitate the introduction of a medium into said last mentioned zonethereby easing the flow of moving metal across said land.

7. In an extrusion apparatus comprising a container assembly, a dieassociated with said assembly in a manner so that material in saidassembly will be caused to flow through an orifice of said die, said diehaving an insert, said orifice being at least partially defined by theinner diameter of said insert, and means for equalizing the radiallyapplied forces exerted on the insert in a radialdirection at the end ofan extrusion stroke wherein the flowing material approaches Zerovelocity, said last-mentioned means including the provision of anannular space around said insert, and means for introducing a mediuminto said space,

8. In an apparatus in accordance with claim 7 wherein said insert isprovide-d with a radially inwardly directed groove on its outerperipheral surface thereby increasing the width of the portion of saidspace.

9. In an apparatus in accordance with claim 7- wherein said insert ismade from a clay bearing material capable of being fired.

10. Apparatus in accordance with claim 7 wherein said insert isreciprocally supported by said die for movement in an axial directionwith respect to said container assembly.

11. Apparatus in accordance with claim 7 wherein said insert isreciprocally supported by said die for movement in an axial directionwith respect to said space, and means including said insert forcontrolling flow of the medium into said space.

8 12. An article of manufacture comprising a die adapted to be utilizedin conjunction with an extrusion apparatus, said die having a boretherethro-ugh, said die having an annular well substantially concentricwith said bore, a removable insert in said well, said insert beingannular, the inner diameter of said insert forming the orifice of saiddie, and the outer periphery of said insert being spaced from an axiallyextending surface of said well by a distance of at least .003 inch, andmeans facilitating the introduction of a flowable medium therebetweenwhereby the radially applied-forces on the insert may be balanced.

13. An article in accordance with claim 12 wherein said insert is madefrom a clay bearing material capable of beingfired.

14. An article in accordance with claim 12 wherein said insert isprovided with a radially inwardly extending groove on its outerperipheral surface.

15. An article in accordance with claim 12 wherein said insert isreciprocally supported by said die for movement in an axial directionwith respect to said annular well.

16. An article in accordance with claim 15 including a flow passage insaid die, said'flow passage being radially inwardly from the outerperipheral surface of said insert, one end of said passage being incommunication with the space between the outer periphery of said insertand the axially extending surface on said well in one reciprocatoryposition of said insert, and said insert interrupting communicationbetween said last mentioned space and said passage in another of itsreciprocatory positions.

17. An article in accordance with claim 12 including a land on said dieconverging toward said orifice, a low pressure zone on said land, and atleast one passag extending through the die in communication with saidlow pressure zone.

18. In an extrusion method comprising the steps of providing anextrusion die with a removable insert, forcing material to flow throughan orifice of the die partially defined by a surface of the insert, andbalancing the radially applied forces'on the insert at the end of theextrusion stroke as the flowing metal approaches zero velocity, saidbalancing step including transmitting the pressure of said materialthrough a flowable medium to an outer peripheral surface of said insert.

19. In an extrusion method comprising the steps of providing anextrusion die with a removable insert, forcing material to flow throughan orifice of the die partially defined by a surface of the insert, andbalancing the radially applied forces on the insert at the end of theextrusion stroke as the flowing metal approaches zero velocity, saidbalancing step includes transmitting the pressure of the metal to theouter periphery of the insert by way of a substantially non compressibleflowable medium,

20. In an extrusion method comprising the steps of providing anextrusion die with an annular insert having an orifice, heating materialwhose cross sectional area is greater than the cross sectional area ofsaid orifice, forcing the heated material to flow through the orifice,and transmitting the pressure of said material through a fiowable mediumas it is flowing toward the orifice to the outer periph'e'ry of saidinsert for balancing the radially applied forces on the insert at theend of the extrusion stroke as the flowing material approaches zerovelocity.

21. In a method in accordance with claim 20 including the step ofrelieving the flowing material of laterally constrictive forces andapplying a flowable medium to the flowing material at the point wherethe flowing material is free from laterally restrictive forces, therebyeasing the extrusion of the material through the orifice.

22. In an extrusion method for extruding hollow metals comprising thesteps of providing a container assembly adapted to support a heatedbillet, providing an extrusion die with a removable ceramic inserthaving an orifice in communication with the interior of said assembly,piercing the billet with a mandrel, forcing material to flow through theorifice and around a mandrel extending through the orifice, andbalancing the radially outwardly directed forces on the insert at theend of the extrusion stroke as the flowing metal approaches zerovelocity, said balancing step including transmitting the pressure ofsaid material through a fiowable medium to the outer periphery of saidinsert.

23. In a method in accordance with claim 22 including the step ofrelieving the flowing metal of radially inwardly and outwardlyrestrictive forces over an annular portion of the periphery areathereof, and introducing a lubricant into said areas.

References Cited by the Examiner UNITED STATES PATENTS Wallace 20710McTear 205--26 Schultz 207-17 Simons 207-l7 Ridgway et a1 205-26 Stulen207--17 Ryshkewitch et al 106-44 Altwicker 20717 MICHAEL V. BRINDISI,Primary Examiner,

CHARLES W. LANHAM, Examiner.

1. IN AN EXTRUSION APPARATUS COMPRISING A CONTAINER ASSEMBLY ADAPTED TOSUPPORT A BILLET THEREWITHIN, A DIE MEANS HAVING AN ORIFICE, RAM MEANSASSOCIATED WITH SAID ASSEMBLY FOR APPLYING PRESSURE ON A BILLET IN THECONTAINER ASSEMBLY TO FORCE THE BILLET TO FLOW THROUGH SAID ORIFICE,MEANS FOR PROVIDING A LOW PRESSURE ZONE WHEREIN THE FLOWING MATERIAL OFTHE BILLET IS FREE OF LATERALLY RESTRICTIVE FORCES, SAID DIE MEANSHAVING AN ANNULAR DIE INSERT MADE